Methods of forming bumps using barrier layers as etch masks

ABSTRACT

Forming an electronic structure may include forming a seed layer on a substrate, and forming a mask on the seed layer. The mask may include an aperture therein exposing a portion of the seed layer, and a barrier layer may be formed on the exposed portion of the seed layer. A bump may be formed on the barrier layer, and the mask may be removed. In addition, portions of the seed layer may be selectively removed using the barrier layer as an etch mask.

RELATED APPLICATION

This application claims the benefit of priority from U.S. ProvisionalPatent Application No. 60/552,051 filed on Mar. 10, 2004, the disclosureof which is hereby incorporated herein by reference in its entirety.

FIELD OF THE INVENTION

The present application relates to the field of electronics, and moreparticularly, to methods of forming interconnection bumps and relatedstructures.

BACKGROUND OF THE INVENTION

C4 (Controlled-Collapse Chip Connection) is a means of connecting IC(integrated circuit) chips to substrates in electronic packages.Moreover, C4 is a flip-chip technology in which the interconnections aresmall solder balls on the chip surface. Because it is an area array, C4technology may provide relatively high densities for chipinterconnections.

C4 technology has used since the 1960s and has proven highly reliable inthe semiconductor field. Historically, PbSn (lead-tin) solder has beenevaporated through a metal mask. In the 1990s, electrochemicalfabrication of C4 interconnections was introduced (See, for example, M.Datta, et al., “Electrochemical Fabrication of Mechanically Robust PbSnInterconnections”, J. Electrochem. Soc., 142, 3779 (1995); U.S. Pat. No.5,162,257 to Yung; and WO 96/30933). Electroplating may be moreextendible than evaporation to small C4-pad dimensions, and may providecloser pad spacing, larger wafers, and/or lower-melting solders (havinga higher content of Sn).

U.S. Pat. No. 5,937,320 discusses barrier layers for electroplated PbSneutectic solder joints. An electrochemically fabricated C4interconnection may have a barrier layer between the electroplatedtin-rich solder bump and the ball-limiting metallurgy that protects theterminal metal in the ball-limiting metallurgy from attack by the Sn inthe solder. The barrier layer may be electroplated through the samephotoresist mask as the solder and thus may not require a separatepatterning step. A thin layer of electroplated nickel may serve as areliable barrier layer between a copper-based ball-limiting metallurgyand a tin-lead (PbSn) eutectic C4 ball. U.S. Pat. No. 6,622,907discusses a sacrificial seed layer process for forming C4 solder balls.The disclosures of U.S. Pat. No. 5,937,320 and U.S. Pat. No. 6,622,907are hereby incorporated herein in their entirety by reference.

SUMMARY OF THE INVENTION

According to embodiments of the present invention, forming an electronicstructure may include forming a seed layer on a substrate, and forming amask on the seed layer wherein the mask includes an aperture thereinexposing a portion of the seed layer. A barrier layer may be formed onthe exposed portion of the seed layer, a bump metal may be formed on thebarrier layer, and the mask may be removed. In addition, portions of theseed layer may be selectively removed using the barrier layer as an etchmask.

The bump metal may be formed subsequent to selectively removing portionsof the seed layer using the barrier layer as an etch mask. Moreparticularly, forming the bump metal may include placing a solid solderpreform on the barrier layer. In addition, selectively removing portionsof the seed layer may include etching portions of the seed layer exposedby the barrier layer using an etch chemistry that etches the seed layerselectively with respect to the barrier layer.

Forming the bump metal may precede removing the mask and selectivelyremoving portions of the seed layer. More particularly, selectivelyremoving portions of the seed layer may include etching portions of theseed layer exposed by the barrier layer using an etch chemistry thatetches the seed layer selectively with respect to the barrier layer andthat etches the bump metal selectively with respect to the barrierlayer. After selectively removing portions of the seed layer, a surfaceportion of the barrier layer may be exposed adjacent the bump metaladjacent an edge of the barrier layer. Moreover, forming the bump metalmay include plating the bump metal on the barrier layer.

The barrier layer may include a material different than the seed layerand different than the bump material. In addition, the seed layer mayinclude an adhesion layer on the substrate and a conductivity layer onthe adhesion layer so that the adhesion layer is between theconductivity layer and the substrate. The adhesion layer may include atleast one of titanium, tantalum, tungsten, chromium, aluminum, copper,iridium, platinum, and/or alloys thereof, and/or nitrides thereof. Theconductivity layer may include at least one of aluminum, copper, nickel,gold, silver, and/or alloys thereof. The barrier layer may include atleast one of nickel, cobalt, platinum, silver, palladium, gold, and/oralloys thereof. For example, the barrier layer may include a layer ofnickel-vanadium (Ni:Va). The bump metal may include at least one ofantimony, silver, bismuth, tin, lead, copper, silver, gold, nickel,zinc, and/or alloys thereof. In addition, an oxidation barrier may beformed on the barrier layer before forming the bump metal, and theoxidation barrier may include a material different than the barrierlayer and different than the bump metal. More particularly, theoxidation barrier may be provided if bump metal is not provided byplating (e.g. placement of a solid solder perform, jetting, printing,etc.). For example, the oxidation barrier may include at least one ofcopper, tin, platinum, palladium, silver, and/or gold. Moreover, each ofthe seed layer, the adhesion layer, the conductivity layer, the barrierlayer, the oxidation barrier, and/or the bump metal may include amulti-layer structure. According to particular embodiments, the adhesionlayer may include a layer of titanium and/or titanium-tungsten; theconductivity layer may include a layer of copper; the barrier layer mayinclude a layer of nickel-vanadium; the oxidation barrier may include alayer of gold; and the bump metal may include solder.

According to additional embodiments of the present invention, anelectronic structure may include a substrate, a seed layer on thesubstrate, and a barrier layer on the seed layer so that the seed layeris between the substrate and the barrier layer. A bump metal may beprovided on the barrier layer so that the barrier layer is between thebump metal and the seed layer. In addition, the barrier layer may definea lip extending beyond the bump metal so that surface portions of thebarrier layer are exposed adjacent the bump metal along an edge of thebarrier layer.

The lip of the barrier layer may extend beyond the seed layer so thatthe seed layer is set back from the lip of the barrier layer between thebarrier layer and the substrate. In addition, the barrier layer mayinclude a material different than the seed layer and different than thebump material. The seed layer may include an adhesion layer on thesubstrate and a conductivity layer on the adhesion layer so that theadhesion layer is between the conductivity layer and the substrate.

The adhesion layer may include at least one of titanium, tantalum,tungsten, chromium, aluminum, copper, iridium, platinum, and/or alloysthereof, and/or nitrides thereof. The conductivity layer may include atleast one of aluminum, copper, nickel, gold, silver, and/or alloysthereof. The barrier layer may include at least one of nickel, cobalt,platinum, silver, palladium, gold, and/or alloys thereof. For example,the barrier layer may include a layer of nickel-vanadium (Ni:Va). Thebump metal may include at least one of antimony, silver, bismuth, tin,lead, copper, silver, gold, nickel, zinc, and/or alloys thereof. Inaddition, an oxidation barrier may be formed on the barrier layer beforeproviding the bump metal, and the oxidation barrier may include amaterial different than the barrier layer and different than the bumpmetal. More particularly, the oxidation barrier may be provided if bumpmetal is not provided by plating (e.g. placement of a solid solderperform, jetting, printing, etc.). For example, the oxidation barriermay include at least one of copper, tin, platinum, palladium, silver,and/or gold. Moreover, each of the seed layer, the adhesion layer, theconductivity layer, the barrier layer, the oxidation barrier, and/or thebump metal may include a multi-layer structure. According to particularembodiments, the adhesion layer may include a layer of titanium and/ortitanium-tungsten; the conductivity layer may include a layer of copper;the barrier layer may include a layer of nickel-vanadium; and the bumpmetal may include solder.

According to still additional embodiments of the present invention,forming an electronic structure may include forming a seed layer on asubstrate, and selectively forming a barrier layer on a portion of theseed layer. More particularly, the barrier layer and the seed layer mayinclude different materials, and the barrier layer may include at leastone of nickel, cobalt, platinum, silver, palladium, gold, and/or alloysthereof. For example, the barrier layer may include a layer ofnickel-vanadium (Ni:Va). Portions of the seed layer may be selectivelyremoved using the barrier layer as an etching mask, and a bump metal maybe provided on the barrier layer opposite the seed layer, and the bumpmetal and the barrier layer may include different materials.

Providing the bump metal, for example, may include placing a solidsolder preform on the barrier layer after selectively removing portionsof the seed layer. In an alternative, the bump metal may include a bumpmetal on a second substrate, and providing the bump metal on the barrierlayer may include bonding the barrier layer with the bump metal on thesecond substrate after selectively removing portions of the seed layer.In still another alternative, providing the bump metal may includeproviding the bump metal on the barrier layer before selectivelyremoving portions of the seed layer. Moreover, selectively removingportions of the seed layer may include etching portions of the seedlayer exposed by the barrier layer using an etch chemistry that etchesthe seed layer selectively with respect to the barrier layer. Inaddition, the seed layer may include adhesion and conductivity layers.

In addition, an oxidation barrier may be formed on the barrier layerbefore providing the bump metal, and the oxidation barrier may include amaterial different than a material of the barrier layer and differentthat a material of the bump metal. More particularly, the oxidationbarrier may be provided if bump metal is not provided by plating (e.g.placement of a solid solder perform, jetting, printing, etc.). Forexample, the oxidation barrier may include at least one of copper, tin,platinum, palladium, silver, and/or gold. Moreover, each of the seedlayer, the adhesion layer, the conductivity layer, the barrier layer,the oxidation layer, and/or the bump metal may include a multi-layerstructure. According to particular embodiments, the adhesion layer mayinclude a layer of titanium and/or titanium-tungsten; the conductivitylayer may include a layer of copper; the barrier layer may include alayer of nickel-vanadium; the oxidation barrier may include a layer ofgold; and the bump metal may include solder.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 and 2 are cross-sectional views of bump formation structuresaccording to embodiments of the present invention.

FIGS. 3 a-f are cross-sectional views illustrating steps of formingelectronic structures according to more embodiments of the presentinvention.

FIGS. 4 a-f are cross-sectional views illustrating steps of formingelectronic structures according to still more embodiments of the presentinvention.

FIGS. 5 a-5 h are cross-sectional views illustrating steps of formingelectronic structures according to still more embodiments of the presentinvention.

DETAILED DESCRIPTION

The present invention now will be described more fully hereinafter withreference to the accompanying drawings, in which embodiments of theinvention are shown. This invention may, however, be embodied in manydifferent forms and should not be construed as limited to theembodiments set forth herein. Rather, these embodiments are provided sothat this disclosure will be thorough and complete, and will fullyconvey the scope of the invention to those skilled in the art.

In the drawings, the thickness of layers and regions are exaggerated forclarity. It will also be understood that when an element such as alayer, region or substrate is referred to as being on another element,it can be directly on the other element or intervening elements may alsobe present. In contrast, if an element such as a layer, region orsubstrate is referred to as being directly on another element, then noother intervening elements are present. Similarly, when an element suchas a layer, region or substrate is referred to as being coupled orconnected to/with another element, it can be directly coupled orconnected to/with the other element or intervening elements may also bepresent. In contrast, if an element such as a layer, region or substrateis referred to as being directly coupled or connected to/with anotherelement, then no other intervening elements are present. As used herein,the term “and/or” includes any and all combinations of one or more ofthe associated listed items. The symbol “/” is also used as a shorthandnotation for “and/or”.

Furthermore, relative terms, such as beneath, upper, lower, top, and/orbottom may be used herein to describe one element's relationship toanother element as illustrated in the figures. It will be understoodthat relative terms are intended to encompass different orientations ofthe device in addition to the orientation depicted in the figures. Forexample, if the device in one of the figures is turned over, elementsdescribed as below other elements would then be oriented above the otherelements. The exemplary term below, can therefore, encompasses both anorientation of above and below.

It will be understood that although the terms first and second are usedherein to describe various regions, layers and/or sections, theseregions, layers and/or sections should not be limited by these terms.These terms are only used to distinguish one region, layer or sectionfrom another region, layer or section. Thus, a first region, layer orsection discussed below could be termed a second region, layer orsection, and similarly, a second region, layer or section could betermed a first region, layer or section without departing from theteachings of the present invention. Like numbers refer to like elementsthroughout.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the invention. Asused herein, the singular forms “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises”and/or “comprising,” when used in this specification, specify thepresence of stated features, integers, steps, operations, elements,and/or components, but do not preclude the presence or addition of oneor more other features, integers, steps, operations, elements,components, and/or groups thereof.

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which this invention belongs. It will befurther understood that terms, such as those defined in commonly useddictionaries, should be interpreted as having a meaning that isconsistent with their meaning in the context of the relevant art andwill not be interpreted in an idealized or overly formal sense unlessexpressly so defined herein.

According to embodiments of the present invention, a process for formingflip chip bumps having relatively precise definition may be provided.According to particular embodiments, a blanket deposition of amultilayer plating seed layer covers the wafer, and a plating templatedefines the bump locations. Selective deposition of a barrier layer andthe bump metals is performed at the template openings. After removal ofthe template, the seed layer is removed using the barrier layer as theetch mask. The barrier layer may comprise a material, such as nickel,different than materials of either the seed layer or a solder layerformed on the barrier layer.

Processes described herein may provide for relatively precise definitionof a base of the bump by using the barrier layer rather than the solderbump as the etch mask. By using the barrier layer as the mask to removethe seed layer, bump formation processes according to embodiments of thepresent invention may allow the formation of larger solder bumps withoutconcern for the loss of dimensional control that may result if the bumpswere used as the etch mask to define the seed layer etch.

As shown in FIG. 1, a bonding structure on substrate 71 may include aseed layer 81 (for example, including adhesion layer 81 a and conductorlayer 81 b), a barrier metal 83, and a bump metal 103. By way ofexample, the adhesion layer 81 a may comprise a metal such as chromium,titanium, tungsten, tantalum, aluminum, copper, iridium, platinum,titanium-tungsten, and/or alloys thereof, and/or nitrides thereof. Forexample, the adhesion layer 81 a may include a layer of titanium and/ortitanium-tungsten. The conductor metal 81 b may comprise a metal such ascopper, aluminum, nickel, silver, gold, and/or alloys thereof. Forexample, the conductor layer 81 b may include a layer of copper. Thebarrier metal 83 may comprise a metal such as nickel, cobalt, platinum,gold, palladium, and/or silver. For example, the barrier metal 83 mayinclude a layer of nickel-vanadium. According to other embodiments, thebarrier metal 83 may include a layer of nickel, and the layer of nickelmay be doped with boron and/or phosphorous and/or the layer of nickelmay be a layer of nickel-vanadium. In addition, an oxidation barrier maybe provided between the barrier metal 83 and the bump metal 103, and theoxidation barrier may include at least one of copper, tin, platinum,palladium, silver, and/or gold. For example, the oxidation barrier mayinclude a layer of gold. More particularly, the oxidation barrier may beprovided if bump metal is not provided by plating (e.g. placement of asolid solder perform, jetting, printing, etc.) to reduce oxidation ofthe exposed surface before providing bump metal thereon.

The bump metal 103 may comprise a metal such as tin, silver, bismuth,antimony, lead, copper, gold, nickel, zinc, and/or alloys thereof.According to particular embodiments, the bump metal 103 may include alead/tin solder. Other layers may also be included in structures (suchas to reduce interdiffusion between the adhesion layer and the conductormetal) according to embodiments of the present invention. Moreparticularly, a layer of a metal such as titanium, tantalum, tungsten,chromium, nickel, iridium, platinum, and/or alloys thereof may beincluded between the conductor metal 81 b and the adhesion layer 81 a.For example, a phased layer of chromium and copper may be includedbetween the conductor metal 81 b and the adhesion layer 81 a.

As further shown in FIG. 1, a sidewall of the mask 101 used to form thebarrier metal 83 and the bump metal 103 (such as by electroplating) maybe sloped at an angle, θ, due to factors such as various processconditions, a Gaussian intensity profile of the light projected throughthe mask, and/or absorption of light by photoresist (used to form themask) during patterning which may reduce the intensity with increasingdepth. Regardless the cause, a plated bump metal 103 may have a slopedsidewall as a result. Using the bump metal 103 as an etch mask to etchthe seed layer 81 may thus involve some uncertainty as to which diameterof the bump metal 103 will define the diameter of the remaining seedlayer or UBM. The mask 101, for example, may include one or more of aphotoimageable polymeric material, a metallic material includingapertures therein, and/or a flexible polymeric material includingapertures therein.

As shown in FIG. 2, the mask 101 may be removed so that sidewalls of thebump metal 103 and the barrier metal 83 and portions of the seed layer81 are exposed. Accordingly, exposed portions of the seed layer 81 maybe removed using the barrier metal 83 as an etch mask. Accordingly, thebarrier metal 83 may be different than the conductor metal 81 b anddifferent than a metal of the adhesion layer 81 a.

Using the barrier metal 83 as the etch mask may require an etchant(s)with relatively high reactivity with the conductor metal 81 b and theadhesion layer 81 a but with relatively low reactivity with the barriermetal 83. With this approach, the edge definition may be improved.

FIGS. 3 a-f are cross-sectional views illustrating steps of formingmetallurgy structures according to embodiments of the present invention.As shown in FIG. 3 a, metal pads 303 (such as aluminum pads) and apassivation layer 301 (such as a silicon oxide layer, a silicon nitridelayer, a polyimide layer, and/or other insulating layers) may beprovided on a substrate 305 (such as a semiconductor wafer includingelectronic devices therein). As shown, via holes in the passivationlayer 301 may expose portions of the metal pads 303.

As shown in FIG. 3 b, a seed layer 307 may be formed on the passivationlayer 301 and on exposed portions of the metal pads 303. By way ofexample, the seed layer 307 may include an adhesion layer 307 a and aconductivity layer 307 b. The adhesion layer may include a layer of ametal such as titanium, tantalum, tungsten, chromium, aluminum, copper,iridium, platinum, and/or alloys thereof and/or nitrides thereof.According to particular embodiments, the adhesion layer 307 a mayinclude a layer of titanium and/or titanium-tungsten. The conductivitylayer 307 b may include a layer of a metal such as aluminum, copper,nickel, gold, silver, and/or alloys thereof. According to particularembodiments, the conductivity layer 307 b may include a layer of copper.The seed layer 307 may also include one or more additional layers, suchas a layer to reduce interdiffusion between the adhesion layer 307 a andthe conductivity layer 307 b. An interdiffusion layer, for example, mayinclude a layer of a metal such as titanium, tantalum, tungsten,chromium, nickel, iridium, platinum, and/or alloys thereof and/ornitrides thereof. According to particular embodiments, an interdiffusionlayer may include a phased layer of chromium and copper between theadhesion layer 307 a and the conductivity layer 307 b.

As shown in FIG. 3 c, a mask 309 may be formed on the seed layer 307thereby exposing portions of the seed layer 307 where bump metal is tobe formed. The mask 309, for example, may be a photoimageable polymericmaterial, a metallic material having apertures therein, and/or aflexible polymeric material having apertures therein. According toparticular embodiments, the seed layer 307 may be used as anelectroplating electrode to electroplate bump metal on portions thereofexposed by the mask 309.

As shown in FIG. 3 d, a barrier metal 311 may be formed on portions ofthe seed layer 307 exposed by the mask 309. Moreover, the barrier metal311 may be a material different than a material(s) used for the seedlayer 307 and different than a material(s) used for the subsequentlyformed bump metal. The barrier metal, for example, may include a metalsuch as nickel, cobalt, platinum, silver, palladium, gold, and/or alloysthereof. According to particular embodiments of the present invention,the barrier metal 311 may include a nickel layer, and the nickel layermay be doped with boron and/or phosphorus, and/or the nickel layer maybe a nickel-vanadium layer. Moreover, the barrier metal 311 may beformed by electroplating, catalytic plating, and/or electrolyticplating.

As shown in FIG. 3 e, a bump metal 313 may be formed on the barriermetal 311. The bump metal 313, for example, may include a metal such asantimony, silver, bismuth, tin, lead, copper, gold, nickel, zinc, and/oralloys thereof. According to particular embodiments of the presentinvention, the bump metal may include a lead/tin solder. Moreover, thebump metal may be formed by electroplating, electrolytic plating, and/orcatalytic plating. In another alternative, the bump metal 313 may beformed by filling the mask aperture(s) with a solder paste and melting(and cooling) the solder paste to fuse the paste into a solid bump.According to other alternatives, the bump metal 313 may be formed byliquid metal jetting or screen printing. If the bump metal 313 isprovided by techniques other than plating, for example, an oxidationbarrier may be formed on the barrier metal 311 before providing the bumpmetal 313, and the oxidation barrier may include at least one of copper,tin, platinum, palladium, silver, and/or gold. The oxidation barrier maybe formed, for example, by plating through the mask 309. Oxidation of anexposed surface can thus be reduced before providing the bump metal 313.

The mask 309 may be removed thereby exposing portions of the seed layer307, and exposed portions of the seed layer 307 may be removed using thebarrier layer 311 as an etching mask, as shown in FIG. 3 f. Inparticular, a wet etch chemistry may be selected that etches the seedlayer 307 selectively with respect to the barrier layer 311.Accordingly, undercutting of the seed layer 307 may occur between thebarrier layer 311 and the passivation layer 301. Moreover, the wet etchchemistry may be such that the bump metal is also etched selectivelywith respect to the barrier layer 311. Accordingly, surface portions ofthe barrier layer 311 may be exposed by the bump metal 313 adjacentedges thereof. More particularly, the bump metal 313 may be sufficientlythicker than the seed layer 307 so that exposed portions of the seedlayer 307 may be removed without removing enough of the bump metal 313to significantly effect performance thereof. The bump metal 313 can thenbe reshaped by melting (i.e. reflow).

In an alternative, the mask 309 may be removed without forming the bumpmetal. Solder can then be applied to one or more of the barrier layers311 by placement of a solid solder preform(s). The solid solderpreform(s) can be bonded to the respective barrier layer(s) 311, forexample, by pressure, heating, and/or melting. Moreover, exposedportions of the seed layer 307 may be removed using the barrier layers311 as an etching mask before solder is provided on the barrier layers311. Solder can then be applied to the barrier layers 311 after removingthe exposed portions of the seed layer 307. As discussed above, anoxidation barrier may be formed on the barrier metal 311 beforeproviding the bump metal 313, if the bump metal 313 is provided as solidsolder preforms. The oxidation barrier, for example, may include atleast one of copper, tin, platinum, palladium, silver, and/or gold.Oxidation of an exposed surface can thus be reduced before providing thebump metal 313. The oxidation barrier, for example, may be platedthrough the mask 309.

While not shown in FIGS. 3 a-f for the sake of clarity, sidewalls of themask 309, the barrier layer 311, and the bump metal 313 may be sloped atan angle θ as discussed above with respect to FIGS. 1 and 2. Moreover,the bump metal 313 can be used to provide electrical and/or mechanicalinterconnection with a next level of packaging such as another substrateand/or a printed circuit board. According to particular embodiments ofthe present invention, the adhesion layer 307 a may include a layer oftitanium and/or titanium-tungsten; the conductivity layer 307 b mayinclude a layer of copper; the barrier metal 311 may include a layer ofnickel-vanadium; an oxidation barrier on the barrier metal 311 mayinclude a layer of gold; and the bump metal 313 may include lead-tinsolder. Moreover, one or more of the above referenced layers may have amulti-layer structure.

FIGS. 4 a-f are cross-sectional views illustrating steps of formingmetallurgy structures according to additional embodiments of the presentinvention. As shown in FIG. 4 a, metal pads 403 (such as aluminum pads)and a passivation layer 401 (such as a silicon oxide layer, a siliconnitride layer, a polyimide layer, and/or other insulating layers) may beprovided on a substrate 405 (such as a semiconductor wafer includingelectronic devices therein). As shown, via holes in the passivationlayer 401 may expose portions of the metal pads 403.

As shown in FIG. 4 b, a seed layer 407 may be formed on the passivationlayer 401 and on exposed portions of the metal pads 403. By way ofexample, the seed layer 407 may include an adhesion layer 407 a and aconductivity layer 407 b. The adhesion layer 407 a may include a layerof a metal such as titanium, tantalum, tungsten, chromium, aluminum,copper, iridium, platinum, and/or alloys thereof and/or nitridesthereof. According to particular embodiments, the adhesion layer 407 amay include a layer of titanium and/or titanium-tungsten. Theconductivity layer 407 b may include a layer of a metal such asaluminum, copper, nickel, gold, silver, and/or alloys thereof. Accordingto particular embodiments, the conductivity layer 407 b may include alayer of copper. The seed layer 407 may also include one or moreadditional layers, such as a layer to reduce interdiffusion between theadhesion layer 407 a and the conductivity layer 407 b. An interdiffusionlayer, for example, may include a layer of a metal such as titanium,tantalum, tungsten, chromium, nickel, iridium, platinum, and/or alloysthereof and/or nitrides thereof. According to particular embodiments, aninterdiffusion layer may include a phased layer of chromium and copperbetween the adhesion layer 407 a and the conductivity layer 407 b.

As shown in FIG. 4 c, a mask 409 may be formed on the seed layer 407thereby exposing portions of the seed layer 407 where bump metal is tobe formed. The mask 409, for example, may be a photoimageable polymericmaterial, a metallic material having apertures therein, and/or aflexible polymeric material having apertures therein. According toparticular embodiments, the seed layer 407 may be used as anelectroplating electrode to electroplate bump metal on portions thereofexposed by the mask 409.

As shown in FIG. 4 d, a barrier metal 411 may be formed on portions ofthe seed layer 407 exposed by the mask 409. Moreover, the barrier metal411 may be a material different than material(s) used for the seed layer407 and different than material(s) used for the subsequently formed bumpmetal. The barrier metal 411, for example, may include a metal such asnickel, cobalt, platinum, silver, palladium, gold, and/or alloysthereof. According to particular embodiments of the present invention,the barrier metal 411 may include a nickel layer, and the nickel layermay be doped with boron and/or phosphorus, and/or the nickel layer mayinclude a layer of nickel-vanadium. Moreover, the barrier layer may beformed by electroplating, catalytic plating, and/or electrolyticplating. In addition, an oxidation barrier may be provided on thebarrier metal 411 before providing bump metal thereon, and the oxidationbarrier may include at least one of copper, tin, platinum, palladium,silver, and/or gold. The oxidation barrier may be formed by platingthrough the mask 409. More particularly, the oxidation barrier mayinclude a layer of gold. An oxidation barrier may be provided, forexample, if bump metal is provided by techniques other than plating(e.g. placement of solid solder performs, jetting, printing, etc.).

The first mask 409 may be removed, and a second mask 410 may be formedso that at least one barrier layer 411 a is exposed and so that at leastone barrier layer 411 b is covered, as shown in FIG. 4 e. A bump metal413 may be formed on the exposed barrier metal 411 a, while the coveredbarrier metal 411 b is maintained free of bump metal. The bump metal413, for example, may include a metal such as antimony, silver, bismuth,tin, lead, copper, gold, nickel, zinc, and/or alloys thereof Accordingto particular embodiments of the present invention, the bump metal 413may include a lead/tin solder. Moreover, the bump metal may be formed byelectroplating, electrolytic plating, and/or catalytic plating. Inanother alternative, the bump metal 413 may be formed by filling themask aperture(s) with a solder paste and melting (and cooling) thesolder paste to fuse the paste into a solid bump. In still otherembodiments, the bump metal 413 may be formed by liquid metal jettingand/or screen printing.

The mask 410 may be removed thereby exposing portions of the seed layer407, and exposed portions of the seed layer 407 may be removed using thebarrier layers 411 a-b as etching masks, as shown in FIG. 4 f. Inparticular, a wet etch chemistry may be selected that etches the seedlayer 407 selectively with respect to the barrier layers 411 a-b.Accordingly, undercutting of the seed layer 407 may occur between thebarrier layers 411 a-b and the passivation layer 401. Moreover, the wetetch chemistry may be such that the bump metal is also etchedselectively with respect to the barrier layer 411 a. Accordingly,surface portions of the barrier layer 411 a may be exposed by the bumpmetal 413 adjacent edges thereof. More particularly, the bump metal 413may be sufficiently thicker than the seed layer 407 so that exposedportions of the seed layer 407 may be removed without removing enough ofthe bump metal 413 to significantly effect the performance thereof. Thebump metal 413 can then be reshaped by melting (i.e. reflow).

While not shown in FIGS. 4 a-f for the sake of clarity, sidewalls of themask 409, the barrier layer 411, and the bump metal 413 may be sloped atan angle θ as discussed above with respect to FIGS. 1 and 2. Moreover,the bump metal 413 can be used to provide electrical and/or mechanicalinterconnection with a next level of packaging such as another substrateand/or a printed circuit board. According to particular embodiments ofthe present invention, the adhesion layer 407 a may include a layer oftitanium and/or titanium-tungsten; the conductivity layer 407 b mayinclude a layer of copper; the barrier metal 411 a-b may include layersof nickel-vanadium; oxidation barriers on the barrier metal 411 a-b mayinclude a layer of gold; and the bump metal 413 may include lead-tinsolder. Moreover, one or more of the above referenced layers may have amulti-layer structure.

As discussed above with respect to FIGS. 4 a-f, a bump metal 413 may beselectively plated on a first barrier metal 411 a, while a secondbarrier metal 411 b is maintained free of bump metal. Accordingly, bumpmetal 413 may be used to provide a solder connection to anothersubstrate (such as a printed circuit board or another semiconductorsubstrate), while the barrier layer 411 b (which is maintained free ofbump metal) may be used to provide different interconnects such as wirebond interconnects.

According to additional embodiments of the present invention, all ofbarrier layers 411 may be maintained free of bump metal until afterremoving exposed portions of the seed layer 407 using the barrier layers411 as etch masks. By way of example, solid solder preforms (such aspreformed solder balls) may be placed on some or all of the barrierlayers 411 after removing exposed portions of the seed layer 407 usingthe barrier layers 411 as etch masks. The solid solder preform(s) can bebonded to the respective barrier layer (s) 411, for example, bypressure, heating, and/or melting. In an alternative, bump metal may beprovided on another substrate to which the substrate 405 is to bebonded, and the barrier layers 411 may be bonded to the bump metalprovided on the other substrate.

According to still additional embodiments of the present invention, bumpmetal 413 may be selectively formed on barrier layer 411 a withoutproviding a second mask 410. More particularly, the mask 409 exposingboth barrier layers 411 a-b may be maintained, and bump metal 413 may beselectively formed on barrier layer 411 a, for example, using selectivemetal jetting and/or selective screen printing into the hole exposingthe barrier layer 411 a without jetting or screen printing into the holeexposing the barrier layer 411 b. Accordingly, the structure of FIG. 4 fmay be provided without requiring the second mask 410. Where one or bothof the barrier layers 411 a-b are exposed to the atmosphere beforeproviding bump metal thereon, oxidation barriers may be provided on thebarrier layers 411 a-b as discussed above. The oxidation barriers, forexample, may include layers of at least one of copper, tin, platinum,palladium, silver, and/or gold, and the oxidation barriers can be platedthrough the mask 409 after plating the barrier layers 411 a-b. Theoxidation barriers, for example, may include layers of gold. Separateoxidation layers, however, may not be required in the barrier layers 411a-b include a metal such as gold, silver, platinum, and/or palladiumthat is resistant to oxidation.

FIGS. 5 a-h are cross-sectional views illustrating steps of formingmetallurgy structures according to additional embodiments of the presentinvention. As shown in FIG. 5 a, metal pads 503 (such as aluminum pads)and a passivation layer 501 (such as a silicon oxide layer, a siliconnitride layer, a polyimide layer, and/or other insulating layers) may beprovided on a substrate 505 (such as a semiconductor wafer includingelectronic devices therein). As shown, via holes in the passivationlayer 501 may expose portions of the metal pads 503.

As shown in FIG. 5 b, a seed layer 507 may be formed on the passivationlayer 501 and on exposed portions of the metal pads 503. By way ofexample, the seed layer 507 may include an adhesion layer 507 a and aconductivity layer 507 b. The adhesion layer 507 a may include a layerof a metal such as titanium, tantalum, tungsten, chromium, aluminum,copper, iridium, and/or platinum, and/or alloys thereof and/or nitridesthereof. According to particular embodiments, the adhesion layer 507 amay include a layer of titanium and/or titanium-tungsten. Theconductivity layer 507 b may include a layer of a metal such asaluminum, copper, nickel, gold, silver, and/or alloys thereof. Accordingto particular embodiments, the conductivity layer 507 b may include alayer of copper. The seed layer 507 may also include one or moreadditional layers, such as a layer to reduce interdiffusion between theadhesion layer 507 a and the conductivity layer 507 b. An interdiffusionlayer, for example, may include a layer of a metal such as titanium,tantalum, tungsten, chromium, nickel, iridium, platinum, and/or alloysthereof and/or nitrides thereof. According to particular embodiments, aninterdiffusion layer may include a phased layer of chromium and copperbetween the adhesion layer 507 a and the conductivity layer 507 b.

As shown in FIG. 5 c, a mask 509 may be formed on the seed layer 507thereby exposing portions of the seed layer 507 where bump metal is tobe formed. The mask 509, for example, may be a photoimageable polymericmaterial, a metallic material having apertures therein, and/or aflexible polymeric material having apertures therein. According toparticular embodiments, the seed layer 507 may be used as anelectroplating electrode to electroplate a barrier metal on portionsthereof exposed by the mask 509.

As shown in FIG. 5 d, a barrier metal 511 may be formed on portions ofthe seed layer 507 exposed by the mask 509. Moreover, the barrier metal511 may include a layer of a material different than material(s) usedfor the seed layer 507 and different than material(s) used for asubsequently provided bump metal. The barrier metal 511, for example,may include a metal such as nickel, cobalt, platinum, silver, palladium,gold, and/or alloys thereof According to particular embodiments of thepresent invention, the barrier metal 511 may include a nickel layer, andthe nickel layer may be doped with boron and/or phosphorus. In additionor in an alternative, the nickel layer may include a layer ofnickel-vanadium. Moreover, the barrier layer may be formed byelectroplating, catalytic plating, and/or electrolytic plating. Inaddition, an oxidation barrier may be plated through the mask 509 on thebarrier metal 511, and the oxidation barrier may include at least one ofcopper, tin, platinum, palladium, silver, and/or gold. Moreparticularly, the oxidation barrier may include a layer of gold.According to particular embodiments, the barrier metal 511 may include alayer of nickel-vanadium, and the oxidation layer may include a layer ofgold. Accordingly, oxidation of an exposed surface can be reduced priorto provide bump metal thereon. Moreover, an oxidation barrier may beconsidered a part of the barrier metal. A separate oxidation barrier maynot be required if the barrier metal 511 includes a metal such asplatinum, palladium, silver, and/or gold that is resistant to oxidation.

The mask 509 may then be removed as shown in FIG. 5 e thereby exposingportions of the seed layer 507, and exposed portions of the seed layer507 may be removed using the barrier layers 511 as etching masks, asshown in FIG. 5 f. In particular, a wet etch chemistry may be selectedthat etches the seed layer 507 selectively with respect to the barrierlayers 511. Accordingly, undercutting of the seed layer 507 may occurbetween the barrier layers 511 and the passivation layer 501. Bump metalmay be provided on the barrier layers 511 (and/or oxidation barriers)before or after removing exposed portions of the seed layer. Accordingto particular embodiments of the present invention, the adhesion layer507 a may include a layer of titanium and/or titanium-tungsten; theconductivity layer 507 b may include a layer of copper; the barriermetal 511 may include a layer of nickel-vanadium; an oxidation barrieron the barrier metal 511 may include a layer of gold; and bump metal513, 513′ may include lead-tin solder. Moreover, one or more of theabove referenced layers may have a multi-layer structure.

In some embodiments of the present invention illustrated in FIG. 5 g,all of the barrier layers 511 (and/or oxidation barriers) may thus bemaintained free of bump metal until after removing exposed portions ofthe seed layer 507 using the barrier layers 511 (and/or oxidationbarriers) as etch masks. By way of example, solid solder preforms 513(such as preformed solder balls) may be placed on some or all of thebarrier layers 511 (and/or oxidation barriers) after removing exposedportions of the seed layer 507 using the barrier layers 511 (and/oroxidation barriers) as etch masks as shown in FIG. 5 g. The solid solderpreforms 513 can be bonded to the respective barrier layers 511 (and/oroxidation barriers), for example, by pressure, heating, and/or melting.In other alternatives, bump metal may be selectively provided on barrierlayers 511 (and/or oxidation barriers), for example, using selectivemetal jetting and/or selective screen printing. The bump metal 513, forexample, may include a metal such as antimony, silver, bismuth, tin,lead, copper, gold, nickel, zinc, and/or alloys thereof. According toparticular embodiments of the present invention, the bump metal 513 mayinclude a lead/tin solder. Moreover, the solid solder performs 513 orother bump metal can be used to provide electrical and/or mechanicalinterconnection with a next level of packaging such as another substrateand/or a printed circuit board. As discussed above, the barrier layers511 may be defined to include oxidation barrier layers if separateoxidation barrier layers are provided thereon.

In other embodiments of the present invention illustrated in FIG. 5 h,all of the barrier layers 511 (and/or oxidation barriers) may thus bemaintained free of bump metal until after removing exposed portions ofthe seed layer 507 using the barrier layers 511 (and/or oxidationbarriers) as etch masks. By way of example, bump metal 513′ may beprovided on another substrate 521 to which the substrate 505 is to bebonded, and the barrier layers 511 (and/or oxidation barriers) may bebonded to the bump metal 513′ provided on the other substrate. The bumpmetal 513′ on the other substrate 521 can be bonded to respectivebarrier layers 511 (and/or oxidation barriers), for example, bypressure, heating, and/or melting. The bump metal 513′, for example, mayinclude a metal such as antimony, silver, bismuth, tin, lead, copper,gold, nickel, zinc, and/or alloys thereof. According to particularembodiments of the present invention, the bump metal 513′ may include alead/tin solder. By way of example, the bump metal 513′ may be providedon respective pads 517 of the substrate 521 by plating, jetting, screenprinting, and/or placement of preformed solder balls prior to matingwith barrier layers 511 (and/or oxidation barriers) of substrate 505.Moreover, the pads 517 of the substrate 521 may include adhesion layers,conduction layers, and/or barrier layers as discussed above with respectto layers 507 a, 507 b, and/or 511 of the substrate 505.

While the present invention has been particularly shown and describedwith reference to embodiments thereof, it will be understood by thoseskilled in the art that various changes in form and details may be madetherein without departing from the spirit and scope of the invention asdefined by the appended claims and their equivalents.

1. A method of forming an electronic structure, the method comprising:forming a seed layer on a substrate; forming a mask on the seed layer,the mask including an aperture therein exposing a portion of the seedlayer; forming a barrier layer on the exposed portion of the seed layer;forming a bump metal on the barrier layer; removing the mask; andselectively removing portions of the seed layer using the barrier layeras an etch mask; wherein forming the bump metal is subsequent toselectively removing portions of the seed layer using the barrier layeras an etch mask.
 2. A method according to claim 1 wherein forming thebump metal comprises placing a solid solder preform on the barrierlayer.
 3. A method according to claim 1 further comprising: beforeforming the bump metal on the barrier layer, forming an oxidationbarrier on the barrier layer wherein the oxidation barrier and thebarrier layer comprise different materials.
 4. A method according toclaim 1 wherein selectively removing portions of the seed layercomprises etching portions of the seed layer exposed by the barrierlayer using an etch chemistry that etches the seed layer selectivelywith respect to the barrier layer.
 5. A method according to claim 1wherein the barrier layer comprises a material different than the seedlayer and different than the bump metal.
 6. A method according to claim5 wherein the seed layer comprises an adhesion layer on the substrateand a conductivity layer on the adhesion layer so that the adhesionlayer is between the conductivity layer and the substrate.
 7. A methodaccording to claim 6 wherein the adhesion layer comprises at least oneof titanium, tantalum, tungsten, chromium, aluminum, copper, iridium,platinum, and/or alloys thereof, and/or nitrides thereof.
 8. A methodaccording to claim 6 wherein the conductivity layer comprises at leastone of aluminum, copper, nickel, gold, silver, and/or alloys thereof. 9.A method according to claim 5 wherein the barrier layer comprises atleast one of nickel, cobalt, platinum, silver, palladium, gold, and/oralloys thereof.
 10. A method according to claim 9 wherein the barrierlayer comprises a layer of nickel-vanadium.
 11. A method according toclaim 5 wherein the bump metal comprises at least one of antimony,silver, bismuth, tin, lead, copper, silver, gold, nickel, zinc, and/oralloys thereof.
 12. A method of forming an electronic structure, themethod comprising: forming a seed layer on a substrate; selectivelyforming a barrier layer on a portion of the seed layer wherein thebarrier layer and the seed layer comprise different materials andwherein the barrier layer comprises at least one of nickel, cobalt,platinum, silver, palladium, gold, and/or alloys thereof selectivelyremoving portions of the seed layer using the barrier layer as anetching mask; and after selectively removing portions of the seed layer,providing a bump metal on the barrier layer opposite the seed layerwherein the bump metal and the barrier layer comprise differentmaterials.
 13. A method according to claim 12 wherein providing the bumpmetal comprises placing a solid solder preform on the barrier layerafter selectively removing portions of the seed layer.
 14. A methodaccording to claim 13 further comprising: before providing the bumpmetal, forming an oxidation barrier on the barrier layer wherein theoxidation barrier comprises a material different than a material of thebarrier layer.
 15. A method according to claim 12 wherein selectivelyremoving portions of the seed layer comprises etching portions of theseed layer exposed by the barrier layer using an etch chemistry thatetches the seed layer selectively with respect to the barrier layer.